Refrigerator defrosting mechanism



Sept. 12, 1950 Filed July 19, 1948 C. B. SHREVE REFRIGERATOR DEFROSTING MECHANISM 2 Sheets-Sheet l \NvgNToR CLIFFORD 5.55am;

Avenue; 5

Sept. 12, 1.950 c. B. SHREVE mmcsmon vnmos'rmc uncmmsu Fi1ed Jul y 19, 1948 2 Sheets-Sheet 2 o REFmGERATION BATTERY L 2 o m E u R a Q... o i 3,. i m C 3 I I 1 N rv \NVENTO \FFORD 5.5mm:

on f

Arm N vs Patented Sept. 12, 1950 REFRIGERATOR DEFROS'I'ING MECHANISM Clifford B. Shreve, Niles, Mich minor to Tyler Fixture Corporation, Niles, Mlcln, a corporation of Michigan Application July 18, 1948, Serial No. 29.485

oclaims.

This invention relates to an electrically controlled heating means for defrosting flnned type refrigerator coils, utilizing heat generated in the coil due to its resistance to the flow of electric current through said coil. Preferably it is concerned .with a timed, automatic, electrically controlled heating means of the character noted used for automatically defrosting refrigerator coils at predetermined times or intervals.

In open display self-service cabinets, which have an extensive use in stores retailing food products, both the refrigerating coil and the merchandise in the cabinet from which customers make their selections, are directly exposed to the air in the store and water vapor is taken from this air and condensed on the coil, with a resultant heavy frost or ice accumulation thereon which, at defrosting, must be removed rapidly so that the cabinet temperature does not rise to a danger point before refrigeration is resumed.

With the usual and conventional refrigerator coil and mechanism the time required for melting and removing the collected frost or ice is dependent upon the length of time necessary for the coil temperature to rise above that of freezing, and also the time element required to melt the frost or ice from the coil before refrigeration can be resumed. This is dangerous, generally, in connection with the merchandise in the cabinets which may discolor or spoil when subjected to an elevated temperature for too long a time.

It is an object and purpose of the present invention to remove the hazard of damaged or spoiled merchandise by the provision of a novel, accelerated means of defrosting coils used in retail store, open refrigerators, and also to combine and associate therewith control means for automatically rendering the defrosting means operative at selected, predetermined intervals of time. The rapid removal of frost or ice from the coils is through an elevation of the temperature thereof which is obtained by the resistance to electric current passing through them. A tubular steel, serpentine coil with associated fins connected to a compressor in the usual and conventional manner, and with refrigerant flow controlled therein by the well known expansion valve are included in an electric circuit for the passage of a low voltage current through the coils, resistance to its passage generating heat for melting and thus removing the collected frost or ice thereon.

An understanding of the invention may be had from the following description, taken in connection with the accompanying drawings, in which Fig. 1 is a representation of my invention showing a form of the electrically controlled resistance heating defrosting means,

Fig. 2 is a diagram of the various electric circuits, controls and timer motors and interrupters for rendering the passage of electric current through the coils automatic at predetermined time intervals, and for interruption of the heating current to prevent excessive rise of temperature in the coils and avoid undue strain upon the battery supplying the current for heating, and

Figs. 3 and 4 are somewhat enlarged elevations of the automatically timed control switches used in these circuits.

Like reference characters refer to like parts in the different figures of the drawings.

The receptacle I, suitably heat insulated, has within it a serpentine coil of tubes 2 with suitable connecting U-bands as shown, upon which fins it are secured to provide a very close contact between the metal of the fins and tubes for best heat exchange relation between them. The usual expansion valve 6, controlled by thermostatic element la, is connected at one end to an inlet pipe 5 from a reservoir 6. The housing of the expansion valve i is connected to one end of the refrigerating coil. A pipe i connects the other end of the coil with the compressor ii, which pumps the refrigerating fluid outwardly through an outlet pipe 9 which is connected with or is shaped between its ends as a coil with fins in, as a radiator, for dissipating heat which is produced in the refrigerating fluid by such compression. Such cooled fiuid, after passing through the radiator, is delivered to the reservoir t. This is a conventional arrangement for a mechanical refrigerating unit, and with my invention substantially no change in structure is made, except that the end of the coil 2 which is connected with the expansion valve housing 4- has a coupling at it which electrically insulates the refrigerating coil 2 from the expansion valve housing 4 and the pipe 5.

One circuit wire I! is connected to the coil 2 near the insulated end thereof and leads to a pole of an electric battery IS. A second circuit wire it is connected to the pipe i as shown, or may be connected to the other end of the coil 2, and terminates at a contact post it. A circuit wire it is connected to the other pole of the electric battery i3 and terminates at a contact post lia, spaced a short distance fromthe post it. The posts are adapted to be electrically joined by a movable contact or switch bar I'I connected with the armature of a solenoid having a winding 18. When the solenoid winding is energized by passage or current, an electric circuit is completed which includes the refrigerating coil 2.

The heat generated through the resistance to passage of current through the steel pipes of the coil 2 elevates their temperature above the freezing point of water, with a resultant accelerated melting of frost or ice which has collected on'the coils and fins 3.

One end of the solenoid coil I8 is connected by a wire IS with an automatic controller which controls the operation of the compressor 8 and the defrosting process. The wire 2| connected to the opposite end of the solenoid winding l8 leads to said controller and in said wire a timed interrupter 22 is located. The compressor starts and stops in accordance with the dictates of a thermostatic bulb 23 located in-the refrigerated area and connected in the usual manner by capillary tube 24 with the controller 20.

In Fig. 1 the automatic controller and the current interrupter are shown, and in Fig. 2 more in detail as to structure and functional operations. Electric current is supplied to the controller through a wire 25 leading from an outside electric supply source to the controller 20, with a return wire 26 connected with one side of the compressor 9. The other circuit wire 21 of the compressor is connected with the other supply circuit wire 28 and also with a battery charger 29 at one pole thereof, the other pole of the battery charger being connected to the circuit wire 25 by a wire 30. Two wires 3| and 32 lead from the battery charger, the first to the pole of the battery l3 with which wire I6 is connected, and the other to the wire l2 which connects to the other pole of the battery.

In Fig. 2, a more detailed diagrammatic representation of the controller and current interrupter is outlined. The timer mechanism includes a motor 33, the main wire 25 leading to one side of the motor and the return wire 34 being connected with the wire 21, which in turn connects with the other of the circuit wires 28 from the outside current source. The motor 33 has a shaft 35 on which a disk 36 and arm 31 are connected, side by side, to turn together. Two switch blades 38 normally springing apart are interposed in the wire 26 and have contacts 39 at their separating ends, said contacts separating when a recess 40 in the disk 36, which is diametrically opposite the outer end of the arm 31, comes opposite the upper contact 39 as shown in Fig. 3. But upon closure of the contacts 39 by a further rotation of the disk 36, the connection of the two parts of the wire 26 is completed. The arm 31 when in its upper position comes against the lower of a pair of spring switch members 4| which carry contacts 42. The contacts 42 are normally separated but are closed when the arm 31 is in the position shown in Fig. 3, at the same time that the contacts 39 are separated, while contacts 39 are closed at all times when the contacts 42 are separated. A wire 43 leads from the lower switch member 4|. A wire 44 from the upper switch member 4| leads to and is connected with the wire 34 which, as previously described, connects with wire 21 and a main current source wire 29.

The interrupter mechanism includes an electric motor 45, having a shaft 46, upon which a disk 41, with portions removed at diametrically opposite sides, to leave flat edges parallel to each other, is in engagement at its edges with the upper of a pair of switch members 48 which have contacts 49 at their separating ends. The contacts are together when the curved edges of the disk 41 bear against the upper switch member 48, but separate when the flattened sides of the member 41 come to said upper switch member 48. The line l9 from solenoid winding i9 is connected with the upper of the switch members 48. The wire 43 leads to one side of I the motor 45. From the other side of the motor a wire 5| connects with the main current inlet wire 25. The lower switch member 48 is connected by a wire 52 with the wire 5| thereby providing connection with the main inlet 25.

The motor 33 turns continuously at slow speed, which may be selectively timed, to close the switch contacts 42 at periodic intervals and simultaneously open the contacts 39. When said contacts 42 are together and at the same time contacts 49 are closed, current from wire 25 through wires 5| and 52, the switch members 48, wire l9, solenoid winding I8 and its connection at its opposite end to the wire 43, is carried through the switch members 4|, the wires 44 and 34 to wires 21 and 28. An electric circuit is completed which energizes the solenoid |8 so as to close the circuit by bar bridging contacts l5 and |5a. This completes a battery circuit through wires I2, the refrigerating coils 2, the wires |4, I6 and 3| to the other side of the battery. Such closure of the circuit causes electric current to pass through the refrigerating coil 2 which rises in temperature because of resistance to current passage.

The rotation of the motor 45 periodically opens the contacts at 49' sothat the flow of the current through the battery circuit is interruptedl' The speed of rotation of the shaft of motor 45 is such that the interruptions may be between one and two minutes in length, and of course, such length of time may be varied. The interruption and breaking of the circuit through the coils 2 permits the temperature of the coils to become more uniform during such period of interruption and, stopping the fiow of electric current from the battery, saves the battery from the dangers of too rapid depletion.

The connection of the battery with a battery charger, which in turn is connected with the main outside current supply, insures that the battery will be maintained charged under substantially all conditions; and that the battery upon any depletion will be recharged when the circuit is broken by separation of the bridging bar I! between the contacts I5 and |5a. Such breaking of the circuit occurs when the arm 37 passes far enough so that the switch members 4| may separate. Simultaneously, the contacts at 39 will be closed for the flow of current to the compressor 9 as dictated by the thermostatic bulb at 23 located within the temperature zone of the refrigerating coil 2, in accordance with conventional practice. The compressor motor is cut out of operation during defrosting periods and a defrosting period does not occur simultaneously with normal refrigeration operations.

With the construction described, not only does the defrosting take place at regular selected time intervals sufliciently close together that too long a time between defrostings does not elapse, but the defrosting is much accelerated, so that the temperature of the food products in a food display case does not rise sufliciently to damage these food products during the defrosting operation. Too severe a strain on the battery I3 and too rapid a depletion of its electrical supply is guarded against. The defrosting can take place only when the regular refrigeration mechanism is made automatically inoperative, such refrigeration mechanism being automatically rendered operative after the defrosting period is over.

The invention is very practical and useful. It is defined in the appended claims and is to be considered comprehensive of all forms of structure coming within their scope.

I claim:

1. In a structure as described, a refrigerating coil on which frost and ice is adapted to collect, an electric circuit including a source of direct electric current in which said coil is included,

switch means normally open for completing or breaking said circuit, means for closing said switch at preselected time intervals and for maintaining the circuit closed for a preselected period of time, and separate circuit interrupting means for periodically separately opening the circuit during such period of time that the first circuit closing means is in closed position.

2. In a structure as described, a refrigerating coil upon which frost and ice is adapted to collect, connections between said coil and an electrically operated refrigerant compressor, one of said connections of the coil thereto including electric insulating material at one end of the coil, an electric circuit wire connected to said end of the coil, a second circuit wire connected to the other end of the coil, a source of electric current to which the first wire is connected, a third wire connected to said source of electric current, circuit closing means between said second and third wires, said circuit closing means being normally open, means for electrically closing said circuit closing means for passage of electric current through said coil to raise the temperature thereof, an electric circuit for said compressor, and means for interrupting flow of electric current to said compressor when the circuit including the refrigerating coil is closed.

3. In a structure of the class described, a refrigerating evaporator coil in a mechanical refrigerating system, said coil being adapted to collect frost and ice at its exterior, an electric stor-- age battery, circuit wires connecting the electric battery with opposite ends of the coil, a make and break switch in one of said wires, said switch being normally open, means for closing said switch including a refrigeration cycle control operablc to close the switch only when the refrigerating compressor is inoperative, and further including a motor driven circuit interrupter interposed in said battery and refrigerating coil circuit, said interrupter including means for breaking said circuit to interrupt current flow through the refrigerating coil from the battery at timed intervals of flow of current through said coil.

4. In a structure as'described, a refrigerating coil on which frost and ice is adapted to collect, an electric circuit including a source of direct electric current in which said coil is included, a make and break switch in one of said wires, means for closing said switch at regular spaced intervals of time and for holding the switch closed for a preselected period of time, circuit interrupting means in said circuit, electrically driven operating means for driving said circuit breaking means to periodically break said circuit during the time that it is closed by said switch and thereafter close it after a predetermined time interval, said making and breaking of the circuit by the last circuit breaking means occurring during the time that the circuit is closed by said circuit closing means.

5. In a structure as described, a refrigerating system including an electrically operated refrigerant compressor and an evaporator coil having resistance to passage of an electric current, an electric circuit for said compressor, an electric circuit connected to respective ends of said coil, timed means for breaking and making said compressor circuit, timed means for making and REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,913,433 Doble, Jr. June 13, 1933 1,998,575 Furnas Apr. 23, 1935 2,086,622 Kagi July 13, 1937 2,281,770 Hoesel May 5, 1942 2,313,390

Newton Mar. 9, 1943 

